1. Field of the Invention
This invention relates to a recording member used for recording by a laser beam and a process for recording comprising using said recording member.
2. Description of the Prior Art
There is known a process for recording an information by focussing a strongly modulated, scanned or deflected laser beam to a spot of a high energy density, irradiating a recording member and thereby selectively removing and/or deforming a part of the recording member by melting and/or vaporizing to produce a record of the information.
This type of recording process can give a real time recording without any post-treatment such as heat development and fixation, and any liquid treating agent, and can produce images of high resolution and high contrast. The recording medium is not sensitive to indoor light, so that no darkroom procedure is necessary, and is suitable for recording electric signals such as output of computers and transmitted time serial signals, and add-on is possible. Therefore, this type of recording process can be used for recording microimages and ultramicroimages, and for computer microfilmer, microfacsimile and phototypesetting plate, and can minify the recording apparatus, elevate the function and improve the image quality.
Conventional recording members used for this type of recording process are those composed of a support and an absorption layer of about 0.1 micron overlying the support and composed of a metal or a semi-metal such as rhodium, bismuth and the like. However, the degree of light reflection of such metal thin film is higher than 50% at the visible region, near infrared region and infrared region. Hence, only less than 50% of the light energy of a laser applied thereto is absorbed to the metal thin layer and such low rate of absorption is not desirable from an efficiency or sensitivity point of view. In addition, when an absorption layer made of a metal having a high thermal conductivity is irradiated with a laser beam, the temperature at the circumference of the irradiated portion becomes high and some deformations occur there due to melting and the like. In general, the recording density or resolution should have the highest value only at the focussed spot and therefore, the deformation at the circumference results in lowering of the recording density and resolution. As is clear from above, when a metal layer is used as a recording layer, the sensitivity and resolution are decreased.
Another drawback of the conventional recording member is as shown below. Since a working distance (a distance between a lens surface and a focus) of an optical system necessary for focussing a laser beam to a beam diameter of less than several microns is usually as short as several hundred microns, the vapor or particles of the recording layer material generated from the recording material when irradiated with a laser sometimes attach to the lens surface resulting in lowering the recording accuracy. Generally the depth of focus is less than several microns and therefore, it is necessary to detect the focussing state, feed the detected result back and maintain a constant focussing state at real time for the purpose of focussing the laser light effectively on the surface of the recording material. The vapor or sputtered particles of the recording layer material sometimes disturb the accuracy of the detection. Further, depending upon the type of the recording material and the irradiating conditions of laser, the vapor or sputtered particles cause a noise which effects a recording information.